Field of the Invention
The present invention relates to an apparatus, a method, and a medium. Specifically, the present invention relates to an apparatus, a method, and a medium for acquiring a high dynamic range image.
Description of the Related Art
It is known generally that the dynamic range of an image capturing sensor that is used in an image capturing apparatus such as a digital camera is narrow compared to the dynamic range of the natural world. Because of this, in the case where a scene having a wide dynamic range (referred to as a high dynamic range, which is abbreviated to “HDR” in the present specification) is photographed by the normal method, blocked up shadows or white saturation occurs. Consequently, various methods are discussed for acquiring HDR image data.
In a general method, an image obtained by photographing the same subject with a long exposure time (long-time exposed image) and an image obtained by photographing the same subject with a short exposure time (short-time exposed image) are acquired. Then, there is a method of acquiring HDR image data by using a long-time exposed image for a dark area and a short-time exposed image for alight area (see Japanese Patent No. 3495768).
Further, there is a method of acquiring HDR image data by determining the exposure time of each pixel based on the results of preliminary photographing by using a sensor capable of controlling the exposure time for each pixel (Japanese Patent Laid-Open No. 2010-136205).
In the methods disclosed in Japanese Patent No. 3495768 and Japanese Patent Laid-Open No. 2010-136205, a gain adjustment in accordance with the exposure time is made to the photographed data that is acquired and HDR combination is performed by switching images that are used for each pixel. At this time, it is required for the luminance response of the image capturing sensor to be linear. However, in the case where there is a nonlinear response in the vicinity of the rise or in the vicinity of saturation of the luminance response of the image capturing sensor as shown in FIG. 12, a gap is produced in the vicinity of the portion of switching and a pseudo contour occurs. In addition, also in the case where noise characteristics are different in the vicinity of the rise or in the vicinity of saturation, a gap between the noise characteristics is produced in the vicinity of the portion of switching and a pseudo contour occurs. Because of this, Japanese Patent No. 3495768 has proposed a method of reducing the occurrence of a pseudo contour by overlapping luminance areas that are acquired at the time of performing photographing while changing the exposure time and by smoothly making the change by weighted addition at the time of switching images. Further, as disclosed in Japanese Patent Laid-Open No. 2010-136205, a method that uses only the linear response area is also disclosed.